I would like to write a generic PHP script that can handle data coming
from any form. How do I know which POST method variables are available?

PHP offers many
predefined variables, like the superglobal
$_POST. You may loop through $_POST
as it's an associate array of all POSTed values. For example, let's
simply loop through it with foreach,
check for empty() values,
and print them out.

All my " turn into \" and my ' turn into \', how do I get rid of all
these unwanted backslashes? How and why did they get there?

Most likely the backslashes magically exist because the PHP directive
magic_quotes_gpc is on.
This is an old feature of PHP, and should be disabled and not relied
upon. Also, the PHP function stripslashes() may be
used to strip the backslashes from the string.

First, an explanation about what this ini setting does. Let's say the
following URL is used:
http://example.com/foo.php?animal=cat
and in foo.php we might have the following
PHP code:

<?php// Using $_GET here is preferredecho $_GET['animal'];

// For $animal to exist, register_globals must be on// DO NOT DO THISecho $animal;

// This applies to all variables, so $_SERVER tooecho $_SERVER['PHP_SELF'];

// Again, for $PHP_SELF to exist, register_globals must be on// DO NOT DO THISecho $PHP_SELF;?>

The code above demonstrates how register_globals creates a lot of
variables. For years this type of coding has been frowned upon, and for
years it's been disabled by default. So although most web hosts disable
register_globals, there are still outdated articles, tutorials, and books
that require it to be on. Plan accordingly.

To be able to use the results of your function in an expression (such
as concatenating it with other strings in the example above), you need
to return the value,
not echo it.

Hey, what happened to my newlines?

<pre><?php echo "This should be the first line."; ?><?php echo "This should show up after the new line above."; ?></pre>

In PHP, the ending for a block of code is either "?>" or
"?>\n" (where \n means a newline). So in the example above,
the echoed sentences will be on one line, because PHP omits
the newlines after the block ending. This means that you need to
insert an extra newline after each block of PHP code to make
it print out one newline.

Why does PHP do this? Because when formatting normal HTML, this
usually makes your life easier because you don't want that newline,
but you'd have to create extremely long lines or otherwise make the
raw page source unreadable to achieve that effect.

When I try to use authentication with IIS I get 'No Input file specified'.

The security model of IIS is at fault here. This is a problem
common to all CGI programs running under IIS. A workaround is
to create a plain HTML file (not parsed by PHP) as the entry page
into an authenticated directory. Then use a META tag to redirect
to the PHP page, or have a link to the PHP page. PHP will
then recognize the authentication correctly. With the ISAPI
module, this is not a problem. This should not affect other
NT web servers. For more information, see:
» http://support.microsoft.com/kb/q160422/ and the manual
section on HTTP Authentication
.

Windows: I can't access files shared on another computer using IIS

You have to change the Go to Internet Information
Services. Locate your PHP file and go to its properties.
Go to the File Security tab, Edit -<
Anonymous access and authentication control.

You can fix the problem either by unticking Anonymous
Access and leaving Integrated Window
Authentication ticked, or, by ticking Anonymous
Access and editing the user as he may not have the access
right.

How am I supposed to mix XML and PHP? It complains
about my <?xml tags!

In order to embed <?xml straight into your PHP code, you'll have to turn off
short tags by having the PHP directive
short_open_tags set to
0. You cannot set this directive with
ini_set(). Regardless of
short_open_tags being on or
off, you can do something like: <?php echo '<?xml'; ?>.
The default for this directive is On.

Where can I find a complete list of variables are available to me
in PHP?

Read the manual page on
predefined variables as it includes a partial list of predefined
variables available to your script. A complete list of available
variables (and much more information) can be seen by calling the
phpinfo() function. Be sure to read the manual
section on variables from
outside of PHP as it describes common scenarios for
external variables, like from a HTML form, a Cookie, and the URL.

How can I generate PDF files without using the non-free and
commercial libraries like
PDFLib? I'd like something that's
free and doesn't require external PDF libraries.

There are a few alternatives written in PHP such as
» FPDF and
» TCPDF.

There is also the Haru extension
that uses the free libHaru external library.

I'm trying to access one of the standard CGI
variables (such as $DOCUMENT_ROOT or
$HTTP_REFERER) in a user-defined
function, and it can't seem to find it. What's wrong?

It's important to realize that the PHP directive register_globals also affects
server and environment variables. When register_globals = off (the
default is off since PHP 4.2.0), $DOCUMENT_ROOT
will not exist. Instead, use $_SERVER['DOCUMENT_ROOT']
. If register_globals = on then the variables
$DOCUMENT_ROOT and
$GLOBALS['DOCUMENT_ROOT'] will also exist.

If you're sure register_globals = on and wonder why
$DOCUMENT_ROOT isn't available inside functions,
it's because these are like any other variables and would
require global $DOCUMENT_ROOT inside the
function. See also the manual page on
variable scope. It's
preferred to code with register_globals = off.

A few PHP directives may also take on shorthand byte values, as opposed
to only integer byte values. What are all the available
shorthand byte options? And can I use these outside of php.ini?

The available options are K (for Kilobytes), M (for Megabytes) and G (for
Gigabytes; available since PHP 5.1.0), these are case insensitive.
Anything else assumes bytes.
1M equals one Megabyte or 1048576
bytes. 1K equals one Kilobyte or
1024 bytes. You may not use these shorthand
notations outside of php.ini, instead use an integer
value of bytes. See the ini_get() documentation for
an example on how to convert these values.

Notă:
kilobyte versus kibibyte

The PHP notation describes one kilobyte as equalling 1024 bytes, whereas
the IEC standard considers this to be a kibibyte instead.
Summary: k and K = 1024 bytes.

Prior to PHP 5.3.4, there was a bug in the network resolving code inside PHP that
caused localhost in all stream related situations to fail if IPv6
was enabled. To work around this issue you can either use "127.0.0.1"
or disable IPv6 resolving in the hosts file.

Here's a simple function that will convert the shorthand values described in point 64.16 to a number of bytes.

I use this to display the maximum size of file uploads to the user, so they don't waste time uploading a huge file only to find that it's too big. (I've been unable to find any browsers that actually support the MAX_FILE_SIZE technique described in chapter 38, and it's certainly not part of any W3C spec, so this is the next best thing.)

Here's how you'd use my function for that purpose (though you might want to abstract this to a function of its own):